Key Experimental Considerations When Evaluating Functional Ionic Liquids for Combined Capture and Electrochemical Conversion of CO2

Ionic liquids (ILs) are considered functional electrolytes for the electrocatalytic reduction of CO2 (ECO2R) due to their role in the double-layer structure formation and increased CO2 availability at the electrode surface, which reduces the voltage requirement. However, not all ILs are the same, considering the purity and degree of the functionality of the IL. Further, there are critical experimental factors that impact the evaluation of ILs for ECO2R including the reference electrode, working electrode construction, cosolvent selection, cell geometry, and whether the electrochemical cell is a single compartment or a divided cell. Here, we describe improved synthesis methods of imidazolium cyanopyrrolide IL for electrochemical studies in consideration of precursor composition and reaction time. We explored how IL with cosolvents (i.e. acetonitrile, dimethylformamide, dimethyl sulfoxide, propylene carbonate, and n-methyl-2-pyrrolidone) affects conductivity, CO2 mass transport, and ECO2R activation overpotential together with the effects of electrode materials (Sn, Ag, Au, and glassy carbon). Acetonitrile was found to be the best solvent for lowering the onset potential and increasing the catalytic current density for the production of CO owing to the enhanced ion mobility in combination with the silver electrode. Further, the ECO2R activity of molecular catalysts Ni(cyclam)Cl2 and iron tetraphenylsulfonato porphyrin (FeTPPS) on the carbon cloth electrode maintained high Faradaic efficiencies for CO in the presence of the IL. This study presents best practices for examining nontraditional multifunctional electrolytes amenable to integrated CO2 capture and conversion technologies for homogeneous and heterogeneous ECO2R.

From Ln2O2S to Ln10OS14: exploring the sulphur spectrum of trivalent lanthanoid oxysulphides

While Ln2O2S oxysulphides have increasingly gained attention due to their structural and optoelectronic properties, an expansive compositional space lies beyond as the sulphur-to-oxygen ratio increases. In these oxysulphides, the compounded effect of the 4f states is manifold in the lanthanoid ions and the changing bonding and environment symmetry enables the tuning of their electronic structure and photophysical properties. Their challenging syntheses have made these materials largely unexplored, but recent efforts have been made to bridge the knowledge gap. In this article we present some of the structural characteristics and photophysical properties of the lanthanoid oxysulphide spectrum LnxOySz.

X-ray absorption spectroscopy insights on the structure anisotropy and charge transfer in Chevrel Phase chalcogenides

The electronic structure and local coordination of binary (Mo₆T₈) and ternary Chevrel Phases (M_xMo₆T₈) are investigated for a range of metal intercalant and chalcogen compositions. We evaluate differences in the Mo L₃-edge and K-edge X-ray absorption near edge structure across the suite of chalcogenides M_xMo₆T₈ (M = Cu, Ni, x = 1-2, T = S, Se, Te), quantifying the effect of compositional and structural modification on electronic structure. Furthermore, we highlight the expansion, contraction, and anisotropy of Mo₆ clusters within these Chevrel Phase frameworks through extended X-ray absorption fine structure analysis. Our results show that metal-to-cluster charge transfer upon intercalation is dominated by the chalcogen acceptors, evidenced by significant changes in their respective X-ray absorption spectra in comparison to relatively unaffected Mo cations. These results explain the effects of metal intercalation on the electronic and local structure of Chevrel Phases across various chalcogen compositions, and aid in rationalizing electron distribution within the structure.

Multi-dimensional designer catalysts for negative emissions science (NES): bridging the gap between synthesis, simulations, and analysis

Negative emissions technologies will play a critical role in limiting global warming to sustainable levels. Electrocatalytic and/or photocatalytic CO2 reduction will likely play an important role in this field moving forward, but efficient, selective catalyst materials are needed to enable the widespread adoption of these processes. The rational design of such materials is highly challenging, however, due to the complexity of the reactions involved as well as the large number of structural variables which can influence behavior at heterogeneous interfaces. Currently, there is a significant disconnect between the complexity of materials systems that can be handled experimentally and those that can be modeled theoretically with appropriate rigor and bridging these gaps would greatly accelerate advancements in the field of Negative Emissions Science (NES). Here, we present a perspective on how these gaps between materials design/synthesis, characterization, and theory can be resolved, enabling the rational development of improved materials for CO2 conversion and other NES applications.

Fe(II) Induced Reduction of Incorporated U(VI) to U(V) in Goethite

Over 60 years of nuclear activities have resulted in a global legacy of radioactive wastes, with uranium considered a key radionuclide in both disposal and contaminated land scenarios. With the understanding that U has been incorporated into a range of iron (oxyhydr)oxides, these minerals may be considered a secondary barrier to the migration of radionuclides in the environment. However, the long-term stability of U-incorporated iron (oxyhydr)oxides is largely unknown, with the end-fate of incorporated species potentially impacted by biogeochemical processes. In particular, studies show that significant electron transfer may occur between stable iron (oxyhydr)oxides such as goethite and adsorbed Fe(II). These interactions can also induce varying degrees of iron (oxyhydr)oxide recrystallization (<4% to >90%). Here, the fate of U(VI)-incorporated goethite during exposure to Fe(II) was investigated using geochemical analysis and X-ray absorption spectroscopy (XAS). Analysis of XAS spectra revealed that incorporated U(VI) was reduced to U(V) as the reaction with Fe(II) progressed, with minimal recrystallization (approximately 2%) of the goethite phase. These results therefore indicate that U may remain incorporated within goethite as U(V) even under iron-reducing conditions. This develops the concept of iron (oxyhydr)oxides acting as a secondary barrier to radionuclide migration in the environment.

Machine Learning Guided Synthesis of Multinary Chevrel Phase Chalcogenides

The Chevrel phase (CP) is a class of molybdenum chalcogenides that exhibit compelling properties for next-generation battery materials, electrocatalysts, and other energy applications. Despite their promise, CPs are underexplored, with only ∼100 compounds synthesized to date due to the challenge of identifying synthesizable phases. We present an interpretable machine-learned descriptor (H_δ) that rapidly and accurately estimates decomposition enthalpy (ΔH_d) to assess CP stability. To develop H_δ, we first used density functional theory to compute ΔH_d for 438 CP compositions. We then generated >560 000 descriptors with the new machine learning method SIFT, which provides an easy-to-use approach for developing accurate and interpretable chemical models. From a set of >200 000 compositions, we identified 48 501 CPs that H_δ predicts are synthesizable based on the criterion that ΔH_d < 65 meV/atom, which was obtained as a statistical boundary from 67 experimentally synthesized CPs. The set of candidate CPs includes 2307 CP tellurides, an underexplored CP subset with a predicted preference for channel site occupation by cation intercalants that is rare among CPs. We successfully synthesized five of five novel CP tellurides attempted from this set and confirmed their preference for channel site occupation. Our joint computational and experimental approach for developing and validating screening tools that enable the rapid identification of synthesizable materials within a sparse class is likely transferable to other materials families to accelerate their discovery.

Stabilizing Hydrogen Adsorption through Theory-Guided Chalcogen Substitution in Chevrel-Phase Mo6X8 (X=S, Se, Te) Electrocatalysts

In this work, we implement a facile microwave-assisted synthesis method to yield three binary Chevrel-Phase chalcogenides (Mo₆X₈; X = S, Se, Te) and investigate the effect of increasing chalcogen electronegativity on hydrogen evolution catalytic activity. Density functional theory predictions indicate that increasing chalcogen electronegativity in these materials will yield a favorable electronic structure for proton reduction. This is confirmed experimentally via X-ray absorption spectroscopy as well as traditional electrochemical analysis. We have identified that increasing the electronegativity of X in Mo₆X₈ increases the hydrogen adsorption strength owing to a favorable shift in the p-band position as well as an increase in the Lewis basicity of the chalcogen, thereby improving hydrogen evolution reaction energetics. We find that Mo₆S₈ exhibits the highest hydrogen evolution activity of the Mo₆X₈ series of catalysts, requiring an overpotential of 321 mV to achieve a current density of 10 mA cm^-2_ECSA, a Tafel slope of 74 mV per decade, and an exchange current density of 6.01 × 10^-4 mA cm^-2_ECSA. Agreement between theory and experiment in this work indicates that the compositionally tunable Chevrel-Phase chalcogenide family is a promising framework for which electronic structure can be predictably modified to improve catalytic small-molecule reduction reactivity.

[Eales' disease with bilateral brain strokes and jaw-closing dystonia]

Eales' disease is an idiopathic occlusive vasculopathy of the retina, which is characterized by extensive peripheral non-perfusion, perivascular sheathing, and neovascularization. It is associated with recurrent vitreous hemorrhages. Both eyes are affected consecutively in 80% to 90% of the patients. In spite of the multiple theories that have been proposed, it continues to have unknown origin and its diagnosis relies on exclusion of other causes of retinal vasculopathy. In some occasions, these patients develop complications of the central nervous system, above all brain infarcts. We present the case of a 38 year old woman with Eales' disease who developed bilateral brain infarcts associated with occlusion or stenosis of the middle cerebral arteries. The cerebral angiography showed beading of the Silvian arteries, suggestive of an underlying inflammatory disorder. Early corticosteroid therapy could avoid contralateral retinal involvement and neurological complications. The patient also presented delayed jaw closing dystonia secondary to basal ganglia infarct which followed a benign course with spontaneous resolution in a few days.

[Lower cranial nerve involvement as the initial manifestation of Lyme borreliosis]

Lyme disease or Lyme borreliosis is an infectious disease transmitted by ticks and caused by Borrelia burgdorferi. Being clinically different from Relapsing Fever it may cause an array of symptoms, specially cutaneous and neurological but also musculoskeletal and cardiac ones. Within the neurologic manifestations of Lyme disease the affectation of low cranial nerves is, to our knowledge, extremely infrequent. We present the clinical case of a 35 years old male whose initial symptoms were low cranial nerve dysfunction with a cerebrospinal fluid compatible with meningitis. Serology against Borrelia burgdorferi both in serum and cerebrospinal fluid was positive.